This invention finds its application in the field of electronics for the manufacture or the repair of components having their inputs/outputs distributed over the bottom or the top surface of said component. The interconnections of these components consist of spherical caps generally made from spherical preforms or balls made of a lead-tin alloy.
Classically, the spherical caps constituting the interconnections are produced according to the following manufacturing sequence:
Deposit of soldering cream or flux on the mounting lands arranged on the substrates or on the preforms,
Transfer of the preforms onto the substrate,
Reflowing in order to solder the preforms onto the mounting lands of the substrate made up by the component.
Generally, the first operation in the transfer phase consists in arranging the balls in orderly fashion in order to be able to deposit them collectively on the substrate, that is, to have one ball opposite each mounting land. Three types of techniques are used to arrange the balls to correspond with the layout of the mounting lands of the component or components:
Parallel stencil technique: This technique consists in using two stencils that can be moved in relative motion to one another so that when the openings of the two stencils correspond, gravity causes the balls to fall onto the substrate placed underneath them, since the balls above are stored in bulk.
Suction technique: This technique consists in sucking up the balls, which are arranged in bulk in a bin, by means of a gripping device. When all the available locations have sucked up a ball, these balls are transferred simultaneously by said gripping device onto said substrate.
Gravity-filled cavities technique: This technique consists in filling cavities corresponding to the design of the substrate for the balls are to be incorporated. As soon as each cavity contains a ball, the transfer operation takes place.
All the preceding techniques have the same disadvantages, namely, the time cycle is too long because it is necessary for each cavity to contain a ball before proceeding with the transfer operation itself, but as this is done using a random arrangement of balls, the time required to arrange the balls is lengthy with respect to the complete cycle time.
Another disadvantage resides in the fact that the level of quality likely to be achieved by these devices is limited, since the probability of having a missing ball remains high and this requires the use of test devices (optical, vacuum sensor, electrical, etc.) in order to verify the presence of all the balls during and after the transfer phase, and consequently increases the cycle time and the complexity of the method for positioning the balls.
Another disadvantage resides in the fact that the excess balls or preforms that return to the storage module create by their motion tiny chips inside the module. These tiny chips could block the suction nozzles of the gripping device or be confused with a preform by the detectors. Furthermore, in order to improve gripping during suction, or in connection with the two other techniques, vibrations are applied to the bulk storage module.
These three techniques described above can be broken down into two method categories:
On the one hand, direct modes in which the transfer operation is accomplished by a transfer apparatus such as a bulk storage module combined with a stencil distributing the preforms directly onto the substrate, or such as a storage device for preforms that passes over the storage cavities so that a preform is placed in each cavity, the substrate coming opposite the filled cavities so that the preforms adhere to the mounting lands provided for this purpose, and
on the other hand, indirect modes, such as the technique using the suction gripping device described above that is inserted between the bulk storage module and the substrate. Thus, in the indirect process, the storage module does not constitute an element of a transfer module, but a module independent of the gripping module.
In order to improve the cycle times of the transfer phase, many processes and devices have been implemented in the prior art. These devices are adaptations of the so-called direct processes.
Thus, for example, a direct transfer device for preforms is described in international application WO 98/43307, this device consisting of a preform storage module combined with a substrate positioning module. One of the features of this transfer device is that a guidance and positioning mechanism is placed between the storage module and the positioning module so that when the transfer module is inverted, the first balls guided and positioned by the positioning module come into contact with the mounting lands provided on the substrate. Although this device solves the problem of positioning the balls with respect to the mounting lands, thereby simplifying the detection systems, the inversion operations and the planned vibrations mean that the tiny chip phenomenon is still present and is likely to be the cause of a faulty transfer. Additionally, the time gained is not particularly meaningful, more particularly because the preform positioning operation is not performed in hidden time but in series with the substrate depositing operation.
Another direct transfer device is described in the Japanese document No. 9-97793. This device consists of a preform storage module combined with a parallel stencil transfer module underneath which is positioned the substrate to receive the balls.
This transfer device is characterized in that a guidance and positioning mechanism for the preforms is inserted between the balls stored in bulk and the stencil transfer module. Although this insertion of a device solves part of the problems involved in conveying balls toward the transfer module, the problem of tiny chips persists as a result of the vibration applied to make the balls to drop (gravity, being the force that pushes the balls toward the stencils). Additionally, the time gained in the time cycle is not significant compared with the cycle time of a device using the parallel stencil technique. Over and above a certain cadence, all the balls do not fall into the cells because they suffer lateral stresses, which affects the quality.
An indirect transfer device is described in Japanese published application JP 07-212023. This device consists of a triple axis preform arrangement matrix whose positions according to the first two axes correspond to the position of the mounting lands of the substrate and define the coordinates of the storage bored hole axes produced in said matrix in which the preforms are arranged. The gripping module, which has suction holes that mirror the positioning of the mounting lands, comes opposite the top end of said matrix to ensure the gripping of the preforms that are positioned and then transfers them onto a substrate. The main feature of this device for providing balls in a collective arrangement is that it is combined with a footprint-by-footprint pusher module for pushing the balls toward the top consisting of rods inserted into the bores near the bottom end of said matrix.
Although this device allows, as part of an indirect mode, an intermediate collective arrangement of the preforms, the availability of said preforms for the gripping device, that is, at the top end of the matrix, is not particularly effective. In effect, when the matrix has not been filled in optimum fashion, the number of preforms per bored holes varies. Thus, the height of the columns of preforms in each bored hole varies, which means that the initial gripping of preforms by the gripping module may not be complete, since some ends of the columns formed by the preforms will not reach the upper extremity of the matrix so that the upper ball is made available to the gripping module. Additionally, another disadvantage of this device for making balls available from a collective preform arrangement phase is that as the pusher module ensuring availability consists of rods that pin the balls to the gripping module to make them available to this module, causing mechanical stress on these balls, stress that can be the source of tiny chips or deformation of the balls. This type of deformation would consequently displace the stroke of the rods necessary to make the balls available in a single layer. Likewise, the use of metal rods adopting a footprint to footprint forward motion (the footprint corresponding to the diameter of the balls) is all the more difficult when the diameter of the balls decreases. Thus, this type of device may not be applicable for certain diameters. In general, the positioning tolerances of the rods inside the bores compared to the diameter of the balls means that this type of pusher module is difficult to use.
Another disadvantage of the device described in this document is that the arrangement matrix is not an independent device, due to the fact that this matrix has the same upper and lower extremity openings necessitating the presence of the pusher module, that is, rods at the lower end of the bored holes. This feature forces the pusher module to wait until its associated matrix is filled to be activated, and said filling thus becomes a serial operation with respect to the provision operation, which reduces the cadence of the manufacturing process using such a device. Thus, although this device uses an indirect method, it does not allow the operations to be completed in hidden time.
Starting from this state of affairs, the applicant conducted research whose aim was to correct the disadvantages of the devices and method cited previously in order to improve both the qualitative and the quantitative aspects of a method for transferring preforms onto a substrate.
Consequently, one target of the invention is to propose, as part of an indirect method, a device that allows certain operations to be performed in hidden time, particularly an operation consisting in causing the preforms to move from a bulk storage condition to an arranged storage condition.
Another target of the invention is to propose, still within the framework of an indirect method, an optimal solution for accomplishing the collective and simultaneous transition of a group of preforms from an ordered and stable condition inside an arrangement matrix to an ordered, stable and available state for a gripping module.
The invention also regards a device making it possible to use a method for depositing interconnection or preforms on a substrate of the type ensures the following phases:
bulk storage of the preforms,
gripping of the preforms in arranged position by an adapted gripping device,
depositing of the preforms on the substrate by the gripping device. This device is characterized in that it consists of at least one triple-axis arrangement matrix for preforms whose positions according to the first two axes correspond to the position of the mounting lands of the substrate and define the coordinates of the storage bored hole axes provided in said matrix in which said preforms are arranged, said bored holes being open at a first extremity so that they permit the passage of said preforms and comprising a closing method at the second extremity preventing the passage of the balls, so that a bulk preform storage module can be placed opposite the open extremities of said bores in order to fill them, said preforms abutting against said closing device at other level of said second extremity of the bored holes.
This device and the matrix characterizing it make it possible to insert between the bulk storage and gripping operations an independent collective arrangement operation for the preforms corresponding to a multiplicity of substrates, so that the gripping device performs only the motion and depositing operation, but no longer the arrangement operation. The ability to make this passage independent from the bulk storage condition to arranged storage state has the advantage of allowing this operation to be carried out in hidden time.
In effect, contrary to the device that implements the indirect method described in the prior art, the presence of a floor on the matrix or of at least one independent method of obstructing one of the extremities of the bores allows the separation of this matrix from all the other modules constituting the rest of the method or the device.
Thus, contrary to the design criteria that have prevailed until now, the applicant endeavored to physically separate the operations according to an indirect method, and to add an operation to the method already known not only so that the gripping device simply performs the gripping operation and not the arrangement operation, but also so that this added operation does not add to but, to the contrary, decreases the cycle time.
In effect, the result of this type of separation of function is that the storage and arrangement operations are performed in advance, and the gripping device performs only a gripping and depositing operation and no longer a gripping/arrangement and depositing operation. Given that the gripping/arrangement and depositing operation constitutes 90% of the cycle time of the preform transfer phase, separating the functions by inserting an independent collective arrangement phase corresponding to a multiplicity of substrates allows a considerable reduction of the time necessary for proper gripping, since the gripping device can thus perform its gripping and depositing motion very quickly.
Separating the functions and adding an additional operation therefore constitute a break with the classic conception of the transfer methods and devices that, until now, privileged, as explained in the prior art, the combination of several functions in a single and same module.
Of course, the other advantages of an added arrangement phase or operation are achieved through enhanced gripping quality as well as through the elimination of any tiny chip produced during gripping due to the fact that the gripping device catches the already-arranged preforms that are provided to the gripping device or devices as they are seized and therefore do not return to bulk storage, but remain arranged.
This device therefore makes it possible to use the maximum positioning potential of transfer machines and to order the balls in hidden time, which frees us from the positioning uncertainties and additional cycle time that this involves.
In effect, withdrawing or providing balls from an ordered and collective presentation corresponding to a multiplicity of substrates considerably reduces the risks of a shortage of balls, which makes it possible to reduce in comparable fashion the time necessary for checking and verifying that all the balls are present. In this way, we reduce the risk of not depositing a ball in a given location. We might say that the collective arrangement device presents an N times smaller risk of forgetting a ball compared to the single-arrangement devices of the prior art (N being the number of balls that may be stacked in the device).
The device of the invention is therefore the perfect adaptation for simultaneously optimizing the qualitative and quantitative aspects of a method for depositing interconnection preforms onto a substrate.
The following description of this invention given by way of non-limiting example and illustrated by drawings allows a better understanding and demonstrates other features and possibilities for this invention.